Which of the following statements about transport through phloem is true?
A. Transport only occurs from the roots to the shoot.
B. It is aided by root pressure.
C. The direction of flow can change at different times if the sources and sinks change.
D. No energy is required.
E. Mostly dissolved starch is transported.
C. The direction of flow can change at different times if the sources and sinks change.
Sources and sinks change through time and therefore, the direction of phloem flow changes.
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Nicotine from cigarette smoke acts as a ligand and associates with specific cells in the nervous system. Nicotine eventually produces feelings of pleasure and well-being. Below are the events that happen in the cellular response to nicotine
Place the events in the correct order to describe the five basic steps in the pathway of a signal transduction system (receptor binding, receptor activation, signal transduction and amplification, response, and termination). A) The acetylcholine receptor is an ion channel, and, when a ligand binds, the ion channel opens. B) An influx of ions causes an action potential, which carries the signal to the reward areas of the brain. C) Nicotine binds to the transmembrane protein that normally binds the neurotransmitter acetylcholine. D) The signal causes release of dopamine in the brain, which causes good feelings. E) Nicotine is quickly eliminated from the body (causing cravings for more cigarettes to produce good feelings). A. C, A, B, D, E B. A, D, B, C, E C. B, A, C, D, E D. C, D, B, A, E
The substance most rich in unsaturated fats is
A. fat that is solid at room temperature. B. butter. C. beef fat. D. bacon grease. E. olive oil.
Four of the five answers listed below are
members of the same group. Select the EXCEPTION.
a. amoeba b. clostridium c. euglena d. water molds e. ciliates
The process of sexual selection tends to occur when females select a trait in males that
a) is an accurate indicator of fitness, e.g., good, healthy genes. b) is associated with unhealthy genes. c) makes them more visible to predators. d) makes them more likely to die immediately after reproducing.